Risk Factors for Recurrent Disc Herniations

The risk factors for a primary disc herniation have been noted to include exposure to repetitive lifting, exposure to vibrations, smoking, and a constitutional weakness of the annular tissue. Isolated trauma or injury has not been found to be a consistent risk factor, occurring in only 0.2% to 10.7% of adults with a herniation. However, Cinotti and colleagues found that 42% of patients with a recurrent disc herniation did relate the onset of radicular pain to an isolated injury or precipitating event. Similarly, Suk and coworkers reported the rate of an isolated injury as a cause of recurrence in 32.1%. This study also noted that 71.4% of the patients with recurrence were males and 57.1% were smokers.

With regard to other potential causal factors, several studies have found that gender, age, obesity, smoking status, level of herniation, and duration of symptoms were generally not associated with higher rates of recurrence. Additionally, the degree of annular incision and the extent of the discectomy (partial or complete) have not been found to affect the potential for recurrence.

One factor that may potentially increase the likelihood of a recurrent disc herniation is diabetes. In general, patients with diabetes have been noted to have lower clinical success rates following the initial lumbar discectomy than do nondiabetic patients. Simpson and associates reported an excellent/good outcome following the initial discectomy of 95% in nondiabetic patients but only 39% in diabetic patients. Mobbs and colleagues reported success rates of 86% in nondiabetic patients and 60% in diabetic patients. Although these clinical outcome differences were generally felt to be attributable to lower quality of life indicators in diabetic patients, Robinson and coworkers investigated the differences in the proteoglycan profile of the discs in the two groups. This study found that diabetic patients had fewer proteoglycans in the disc material, potentially increasing their susceptibility to recurrent disc prolapse.

Another proposed risk factor is the configuration of the initial disc herniation. Grane and colleagues and Suk and associates noted that preoperative disc configuration does not affect the rate of recurrence. Alternatively, Carragee and coworkers prospectively evaluated herniated disc configurations along with the rate of reherniation and the rate of reoperation and noted an association between the two. Disc herniations were divided into four shaped-based groups: (1) fragment-fissure herniations (disc fragment and small annular defect), (2) fragment-defect herniations (large disc fragment with massive posterior annular tear), (3) fragment contained discs (incomplete annular tear), and (4) absence of fragment-contained herniations (annular prolapse). Of the four groups, the fragment-fissure herniations (group 1) were associated with the best outcomes, the lowest rate of reherniation (1%), and required the fewest reoperative procedures (1%). Those with annular prolapse (group 4) were associated with the poorer clinical outcomes, with 38% of patients experiencing recurrent or persistent symptoms.

Evaluation of Recurrent Disc Herniation

The patient who presents with a recurrent disc herniation has generally had a period of clinical improvement following the initial discectomy procedure. A retrospective review of 28 patients with recurrent disc herniation found a pain-free interval ranging from 7 to 168 months (mean of 60.8 months). Patients typically report radicular signs and symptoms similar or identical to those identified in their preoperative clinical state.

Pathologic changes in the ventral epidural space may reflect mass effect due to perineural scarring or recurrent disc herniation. Scarring is most pronounced before 9 months and primarily involves the annulus fibrosus. The scar may surround the nerve roots and cause symptoms by means of neural tension, decreased axoplasmic transport, restriction of blood flow, or of venous return.

Magnetic resonance (MR) imaging, with and without gadolinium contrast, is the preferred imaging modality for the assessment of a recurrent disc herniation. The use of contrast material helps to differentiate normal postoperative anatomic changes from a recurrent herniation. Peridural scarring will typically enhance heterogeneously because of its vascular supply. A recurrent disc herniation usually appears as a polypoid mass with a low signal on T1- and T2-weighted sequences. It is usually contiguous with the parent disc unless sequestered. There can be a hypointense rim of the posterior longitudinal ligament and outer annular fibers that outline the herniation. This rim will enhance with contrast administration ( Fig. 94-1 ). The disc itself will not enhance because it has no blood supply.

Sagittal plane ( A ) and axial plane ( B ) magnetic resonance images following administration of contrast material demonstrating a recurrent disc herniation on the left side at the L4-5 level. The disc fragment is surrounded by a rim of enhancing scar tissue (arrows). The disc fragment itself does not enhance.

MR findings will vary according to the time period the study is obtained relative to the primary procedure. In the early (0 to 6-month) postoperative period, MR imaging demonstrates a high signal intensity band extending from the nucleus pulposus to the site of annular disruption. This is particularly noticeable in the first 2 months following surgery. The annulus is typically hyperintense and the nucleus hypointense. There is loss of disc space height. The end plates and marrow will frequently have a low signal on T ₁ -weighted and a high signal on T ₂ -weighted images, suggesting inflammation and edema. The anterior epidural space initially reveals an increase in soft-tissue mass, evidence of tissue disruption, edema, and hemorrhage, with the appearance of mass effect.

Nerve root enhancement with gadolinium in the first few months following surgery is normal. This typically indicates a breakdown of the blood-nerve barrier but usually resolves within 6 months. Postoperative changes at the laminectomy site depend on the extent of surgery, ligamentum flavum removal, and whether a fat graft was placed in the epidural space. Facet joint enhancement occurs as a local response to dissection and persists long (> 6 months) after surgery in more than half of the patients in whom imaging is performed.

Other later findings on MR include a low-intensity signal band in the disc space, which typically represents a healing annular defect. The mass effect seen earlier in the anterior epidural space may have resolved or may persist as a masslike scar. The laminotomy defect contains mature scar with peripheral enhancement identifying granulation tissue.

Retraction of the thecal sac toward a soft-tissue lesion is suggestive of scar, whereas displacement away from such a mass is suggestive of recurrent herniated disc material. Although a pseudomeningocele may also be seen as mass at the prior surgical site, its signal characteristics are more consistent with cerebrospinal fluid on both T1- and T2-weighted images. It may also be associated with an enhancing fibrous capsule.

Despite the imaging advantages provided by MR over other techniques, there can be a significant degree of discordance between MR findings and intraoperative findings. This discordance can occur in 18% to 33% of cases proven surgically. As with the initial procedure, the successful outcome of any surgery for recurrent disc herniation depends on a close correlation between the clinical and radiographic findings.